The present invention relates to apparatus comprising planar elements, e.g. of a semi-rigid material such as corrugated cardboard, the elements being able to be assembled together to form a structure, e.g. a cross brace of a bottle crate. Although the invention is not so restricted, it relates more particularly to apparatus in which the assembled elements, by being pivoted, can be brought flat against one another and can be locked in the assembled position both when flat and after being opened out.
A cross brace for a bottle crate consists of sheets of cardboard or corrugated carboard notched at regular intervals over some of their height with slits, into which the corresponding slits of similar sheets are engaged so as to form a unit which, together with a cardboard case in which it is accommodated, defines a plurality of identical receptacles for bottles.
Cross braces can be stored flat after assembly. It is also common to accommodate them in advance in American-style cases in which they are used, the cross braces sometimes being fixed by means of glueing to an inner face of these cases. In the latter situation, it is the cases themselves which are stored flat, together with the cross braces which they contain.
It is therefore important to ensure, both when the cross braces are installed in the cases and when they are opened out, that there is no risk of their component elements coming away from one another.
The same applies when the case is full of bottles, in particular when the cross braces used are of the so-called "economy" type, in which the receptacles of the cross braces only protect the bottles up to their shoulder.
It is therefore desirable that the component elements of the cross brace should be locked, once assembled, whatever their relative positions and whatever the manipulations to which they are subjected during the time when they are opened out or after this.
To achieve this, it has already been proposed in French Patent Specification No. 2,154,339 to lock, in the assembled position, two sheets of cardboard having notches in which the sheets are interleaved with one another, at the same time giving the notches of one of the sheets a non-rectilinear profile defining a tooth which can be engaged in a slit made in the corresponding position in the other sheet.
Such a system ensures excellent locking of two sheets joined together, when they are in the position of use, that is to say when they are perpendicular to one another. In contrast to this, however, when the sheets are folded flat, the teeth can very easily escape from their slits, simply because the sheets slide in contact with one another, and there is no security in this position.